Download Results of Phototherapeutic Keratectomy in the Management of Flap

Results of Phototherapeutic Keratectomy in
the Management of Flap Striae after LASIK
Roger F. Steinert, MD,1,2 Amin Ashrafzadeh, MD,1,3 Peter S. Hersh, MD4
Objective: To evaluate the efficacy of phototherapeutic keratectomy (PTK) in reducing or resolving visually
significant surface irregularities resulting from flap striae after LASIK.
Design: Retrospective, noncomparative case series.
Participants: Twenty-three eyes of 22 patients with flap striae after LASIK and reduced best-corrected
visual acuity or visual symptoms that resolved with diagnostic contact lens fitting treated between January 2001
and April 2002 with at least 1 month of follow-up. The mean follow-up interval was 134 days (range, 30 –354
days).
Intervention: Transepithelial PTK.
Main Outcome Measures: Uncorrected visual acuity (UCVA), resolution or reduction of preoperative symptoms, corneal haze, and best spectacle-corrected visual acuity (BSCVA).
Results: Mean BSCVA and UCVA improved significantly from 20/32 and 20/48 to 20/22 and 20/33
(P⬍0.0001 and P ⫽ 0.027), respectively, after PTK. There was a significant mean hyperopic shift of 0.88 diopters
(D; P ⫽ 0.002, range, ⫺1.38 to ⫹3.88 D). Fourteen eyes (61%) were clinically clear, 6 eyes (23%) had trace haze,
and 3 eyes (16%) had 1⫹ haze at the last follow-up visit. Mean spherical equivalent refractive error before LASIK
was ⫺7.23 D (range, ⫺2.88 to ⫺13.55 D). Twenty-two of 23 eyes had significant qualitative resolution or
reduction of preoperative visual symptoms.
Conclusions: In cases of visually significant LASIK flap striae, PTK is effective in improving best-corrected
visual acuity and reducing visual symptoms. High myopia may be a risk factor for development of visually
significant microstriae. Development of anterior stromal haze did not exceed 1⫹ density and was not correlated
to either the number of laser pulses or the length of the follow-up period. Ophthalmology 2004;111:740 –746 ©
2004 by the American Academy of Ophthalmology.
A safe and effective LASIK procedure requires creating,
lifting, repositioning, and healing of a corneal flap that does
not degrade the corneal optics. Wrinkles in the flap may
cause loss of best-corrected visual acuity and symptoms
such as multiplopia resulting from optical aberrations. Strategies to reduce or eliminate flap wrinkles include lifting the
flap, hydration, stroking, smoothing, suturing, heating, use
of a bandage contact lens, and discarding the flap with or
without replacement lamellar keratoplasty.1– 8
A useful clinical classification of flap wrinkles distinguishes between macrostriae and microstriae. Macrostriae
are large, full-thickness folds in the LASIK flap, usually
Originally received: October 21, 2002.
Accepted: June 25, 2003.
Manuscript no. 220854.
1
Center for Eye Research and Education, Boston, Massachusetts.
2
Harvard Medical School, Boston, Massachusetts.
3
Tufts University School of Medicine, Boston, Massachusetts.
4
Department of Ophthalmology, University of Medicine and Dentistry of
New Jersey, Newark, New Jersey.
Presented at: American Society of Cataract and Refractive Surgery meeting, June, 2002; Philadelphia.
Authors have no proprietary interest in any product or technique discussed
in this article.
Correspondence to Roger F. Steinert, MD, Ophthalmic Consultants of
Boston, 50 Staniford Street, Suite 600, Boston, MA 02114. E-mail:
[email protected].
740
© 2004 by the American Academy of Ophthalmology
Published by Elsevier Inc.
occurring spontaneously in the first postoperative day after
direct corneal trauma or later. Characteristically, macrostriae are readily visible at the slit-lamp biomicroscope, with
a “washboard” appearance of parallel or semiparallel lines.
If detected and treated acutely by repositioning the flap,
macrostriae usually resolve; if left untreated, however, these
folds may become fixed and unresponsive to conservative
measures.
Microstriae, in contrast, are finer, randomly directed
wrinkles in the anterior cornea. Most microstriae are not
optically significant because of the masking effect of the
overlying epithelium. Microstriae are best seen with retroillumination (Fig 1). Optically significant microstriae generally are not detectable on corneal topography color maps
but may disrupt the placido mire reflection pattern. After a
small amount of fluorescein is placed in the tear film, a
characteristic “negative” staining pattern of reduced fluorescence over the microstriae9 resulting from disruption of
the tear film is helpful in identifying optically significant
microstriae (Fig 2).
Excimer laser phototherapeutic keratectomy (PTK) is
successfully used in the treatment of numerous corneal
surface irregularities, including anterior basement membrane dystrophy,10 Bowman membrane dystrophies, anterior stromal dystrophies,11 superficial corneal scars,12 and
Salzmann’s nodular degeneration.13,14 We investigated the
ISSN 0161-6420/04/$–see front matter
doi:10.1016/j.ophtha.2003.06.015
Steinert et al 䡠 Phototherapeutic Keratectomy for Flap Striae
Figure 1. Slit-lamp retroillumination photomicrograph of microstriae.
Figure 2. “Negative staining” pattern of fluorescein in the tear film resulting from disruption by microstriae.
Figure 3. Sequential operative photographs of the epithelial fluorescence pattern seen during phototherapeutic keratectomy (PTK) for microstriae. A,
With successive pulses, epithelial fluorescence over the most highly elevated striae disappears as the thinnest epithelium becomes fully ablated. Reprinted
with permission from Roger F. Steinert, MD. PTK treatment of chronic flap striae. Refractive Surgery Quarterly 2003;2(4):2⫺3. ©2003 Slack Inc. B, With
further pulses, the epithelium between the striae recedes, along with a further reduction in fluorescence. C, At the end of the transepithelial phase of the
PTK, most of the epithelium is removed, with only minimal residual fluorescence in the areas of thickest epithelium between the striae.
Figure 4. Schematic diagram of the mechanism of reduction in optical disturbance of striae by transepithelial phototherapeutic keratectomy (PTK). Rx
epi ⫽ transepithelial treatment. Reprinted with permission from Roger F. Steinert, MD. PTK treatment of chronic flap striae. Refractive Surgery Quarterly
2003;2(4):2⫺3. ©2003 Slack Inc.
efficacy of PTK to improve corneal optics in the presence of
chronic macrostriae and microstriae. A MEDLINE literature search did not reveal any previous reports of this
technique for treatment of microstriae
Patients and Methods
Patients were either referred after LASIK treatment elsewhere or
had been treated primarily by the authors. All treated eyes exhib-
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Ophthalmology Volume 111, Number 4, April 2004
Table 1. Patient Characteristics
Patients
Eyes
Analysis
Age
(yrs)
22 patients
14 female
8 male
23 eyes
13 right eyes
10 left eyes
Mean
Median
Standard deviation
Minimum
Maximum
44
46
7
30
56
Pre-LASIK Refraction
Pre-LASIK K
Sphere
Cylinder
SE
Vertical K
Horzizontal K
Average K
⫺6.81
⫺6.50
2.90
⫺13.30
⫺2.00
⫺0.84
⫺0.50
0.96
⫺3.25
0.00
⫺7.23
⫺7.13
2.80
⫺13.55
⫺2.88
45.00
44.50
1.82
41.12
48.75
43.84
44.00
1.39
41.50
47.00
44.42
44.25
1.48
41.31
46.83
K ⫽ keratometric power; SE ⫽ spherical equivalent.
ited flap striae and either loss of best spectacle-corrected visual
acuity (BSCVA) or symptoms such as hazy view, ghost images,
monocular multiplopia, or nighttime glare. Patients often described
a fleeting clear view immediately after a blink or placement of
artificial tears in the eye.
All patients underwent a complete preoperative eye examination. Specific attention was given to uncorrected visual acuity
(UCVA), BSCVA, manifest and cycloplegic refractions, corneal
topography, and examination of the tear film staining pattern.
Specific details of the patient symptoms were delineated. If the
patient’s symptoms could not be resolved with refraction, the next
step was to place a soft contact lens to neutralize the optical
significance of the microstriae. If a soft contact lens failed to
improve the symptoms, a hard contact lens refraction was performed. Patients were selected for PTK only if their symptoms
significantly improved or fully resolved with the clinic trial of the
contact lenses.
Before surgery, patients received 2 to 10 mg diazepam and
drops of topical antibiotics, either ofloxacin (Ocuflox; Allergan,
Irvine, CA) or levofloxacin (Quixin; Santen, Napa, CA). A broadbeam excimer laser programmed for PTK with an optical zone of
6.5 mm (Summit Apex Plus [Alcon Summit Autonomous, Orlando, FL] or Star S3 [VISX, Sunnyvale, CA]) was used in all
cases. The nominal depth per pulse specified by the manufacturer
is 0.24 ␮m per pulse with the Summit laser and 0.25 ␮m per pulse
with the VISX laser.
Transepithelial PTK was used, monitoring the pattern of epithelial fluorescence through the operating microscope. Because
epithelium is thinnest over the elevated ridges of the striae, the
initial epithelial breakthrough, heralded by the loss of fluorescence, typically had the pattern of the underlying striae (Figs 3, 4).
Phototherapeutic keratectomy was continued until epithelial fluorescence began to recede between striae. A thin layer of medium
viscosity artificial tears (Refresh Plus; Allergan) then was applied
with a lightly moistened surgical spear, and PTK was resumed to
decrease further the height of the striae. The goal was to achieve
reduction but not elimination of all striae. In a typical treatment,
the transepithelial phase was completed with 180 to 220 pulses,
and a total of 80 to 100 further pulses were applied with the
masking artificial tears. In the second phase of the PTK in which
artificial tears were used, 8 to 10 laser pulses were delivered, and
then the artificial tears were reapplied with a lightly moistened
surgical spear sponge to reestablish a thin layer of masking fluid.
Because much of the laser energy is absorbed by the masking fluid,
it is impossible to calculate the depth of stromal ablation, but it
probably is less than 10 ␮m.
On completion of the procedure, 1 drop of prednisolone acetate
1% (Pred Forte; Allergan) and 1 drop of one of the above antibiotics were placed. A soft bandage contact lens was placed (Model
66, medium base curve; Bausch & Lomb, Rochester, NY). The
patient was instructed to use the steroid and antibiotic drops 5
minutes apart, 4 times daily for the next 5 days. Patients were
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examined early in the postoperative period, at a minimum of day
1 and days 3 to 5. The soft contact lens was removed when
epithelial coverage was achieved, and the patient was instructed to
use a nonpreserved or rapid deactivating preservative ocular surface lubricant for a minimum of every 2 hours while awake for at
least the first postoperative month.
At the 1-month and subsequent postoperative examinations, a
full eye examination along with manifest refraction and notation of
patient symptoms was performed.
Statistical analysis was by paired t test (Microsoft Excel 2000;
Microsoft Corporation, Redmond, WA).
Results
Thirteen right eyes (57%) and 10 left eyes (43%) of 14 female
patients (64%) and 8 male patients (36%) underwent PTK. One
patient underwent PTK in both eyes. The mean patient age was 44
years (range, 30 –56 years).
Patient characteristics are summarized in Table 1. The mean
spherical equivalent refractive error before LASIK was ⫺7.23
diopters (D; range, ⫺2.88 to ⫺13.55 D). The corneal keratometric
power before LASIK was available for 17 of the 23 eyes. The
mean vertical keratometric power was 45.00 D, the mean horizontal keratometric power was 43.84 D, and the mean overall keratometric power was 44.42 D (range, 41.31– 46.83 D). The difference in the vertical versus horizontal keratometric corneal powers
was statistically significant (P ⫽ 0.002). Fifteen of 17 eyes (88%)
had steeper vertical meridians, and 2 eyes (12%) had steeper
horizontal meridians.
Treatment history is detailed in Table 2. The average interval
between the primary LASIK and PTK was 307 days (range,
19 –992 days). The mean follow-up interval after the PTK (to the
last examination or any other subsequent intervention) was 134
days (range, 30 –354 days). Before PTK, eyes 3, 7, and 18 had 1
flap refloat, and eyes 8 and 20 had 2 flap refloats. Eye 6 had a flap
refloat and a subsequent Donnenfeld heating treatment. Eye 15 had
a flap refloat followed by a second refloat combined with epithelial
debridement. Ten eyes had undergone LASIK retreatments before
Table 2. Treatment Intervals
Analysis
LASIK to
Phototherapeutic
Keratectomy
(days)
After
Phototherapeutic
Keratectomy
(days)
Mean
Median
Standard deviation
Minimum
Maximum
307.00
285.00
250.00
19.00
992.00
134
106
81
30
354
Steinert et al 䡠 Phototherapeutic Keratectomy for Flap Striae
Table 3. Changes in Best Spectacle-corrected Visual Acuity
Best Spectacle-corrected
Visual Acuity before
Phototherapeutic
Keratectomy
Best Spectacle-corrected
Visual Acuity after
Phototherapeutic
Keratectomy
Analysis
Snellen
Decimal
Snellen
Decimal
Safety
Index
Improvement in Lines
of Snellen Acuity
Mean
Median
Standard deviation
Minimum
Maximum
20/32
20/30
0.63
0.66
0.20
0.29
1.00
20/22
20/20
0.90
1.00
0.21
0.50
1.33
1.55
1.52
0.58
0.76
2.80
1.70
2
1.66
⫺1
5
20/70
20/20
20/40
20/15
PTK, 8 with lifting of the original flap and 2 with microkeratome
cutting of a new flap. Two eyes (eyes 3 and 19) had been noted to
have minor nonvision impairing microstriae before LASIK retreatment, and visually impairing microstriae developed afterward.
After the PTK treatment, 4 eyes had subsequent LASIK retreatments by lifting the flap that had been treated by PTK. Three
eyes (eyes 1, 5, and 16) were treated successfully with no redevelopment of microstriae afterward. In 1 eye (eye 19) with a
known very thin primary flap, a frank buttonhole developed with
relifting; retreatment was aborted.
Mean BSCVA improved significantly from 20/32 (0.63) before
PTK to 20/22 (0.90) after PTK (P⬍0.0001; Table 3). Uncorrected
visual acuity improved significantly from a mean of 20/48 (0.42)
before PTK to 20/33 (0.60) after PTK (P ⫽ 0.027; Table 4).
Phototherapeutic keratectomy improved BSCVA in 21 of 23
eyes (Figs 5, 6). Uncorrected visual acuity also improved in most
patients, although this was not a primary goal of the PTK treatment
(Fig 7). The mean safety index was 1.70, calculated as decimal
BSCVA value after PTK divided by decimal BSCVA value before
PTK.15 Two eyes (eyes 15 and 19) in this study each had a 1-line
loss of BSCVA. In eye 15, some macular pigment epithelial
changes developed that were consistent with myopic degeneration.
This patient noted improvement in vision symptoms after PTK,
even though a hard contact lens refraction did not improve her
BSCVA. Eye 19 had a very thin flap (77 ␮m) initially. This eye
had minor microstriae that became visually significant after a
flap-lift enhancement procedure. The eye then underwent PTK,
and mild irregular astigmatism and 1⫹ haze developed.
The mean spherical equivalent manifest refraction showed a
hyperopic shift of ⫹0.88 D (range, ⫺1.38 to ⫹3.88 D; P ⫽ 0.002;
Table 5). A small mean reduction of 0.14 D of absolute cylinder
(range, ⫺2.00 to ⫹1.50 D) occurred that was not statistically
significant.
Table 6 tabulates the operative parameters. Total pulses averaged 286 (range, 163–348 pulses). The transepithelial phase was
recorded in 20 of 23 eyes, with a mean of 196 pulses (range,
60 –289 pulses). Flap thickness measurements determined by ul-
trasonic pachymetry were available for 9 of 23 eyes from the
primary surgery. Eye 1 had LASIK retreatment after PTK with flap
thickness measurement at that time. Including eye 1, the mean flap
thickness was 150 ␮m (range, 77–196 ␮m).
Table 7 lists the clinical haze ratings at the last follow-up
examination and the total number of PTK laser pulses. Fourteen
eyes (61%) were completely clear, 6 eyes (23%) had trace haze,
and 3 eyes (16%) had 1⫹ haze. The mean total number of laser
pulses for patients with haze and without haze was 294 (range,
235–348 pulses) and 281 (range, 163–321 pulses), respectively;
the difference approached but did not reach statistical significance
(P ⫽ 0.08). Stromal pulses calculated mathematically as the difference between total number of pulses and the epithelial phase
pulses also are reported. The mean number of stromal pulses in
eyes with haze (100 pulses) and without haze (91 pulses) was not
significantly different (P ⫽ 0.69). The mean follow-up period for
patients with haze and without haze was 100 days (range, 48 –189
days) and 130 days (range, 30 –354 days), respectively; the difference was not statistically significant (P ⫽ 0.13).
Discussion
Phototherapeutic keratectomy directly reduces the anterior
elevations of the striae, thereby reducing or eliminating the
optical disruption of the tear film. The smoothing effect of
the laser pulses is aided by the masking effect of the
epithelium in the transepithelial phase and the use of artificial tears as a masking agent after the laser pulses penetrate through the basal epithelium. Twenty-one of 23 eyes in
this series experienced improvement in BSCVA and reduc-
Table 4. Change in Uncorrected Visual Acuity
Uncorrected Visual
Acuity before
Phototherapeutic
Keratectomy
Uncorrected Visual
Acuity after
Phototherapeutic
Keratectomy
Analysis
Snellen
Decimal
Snellen
Decimal
Mean
Median
Standard deviation
Minimum
Maximum
20/48
20/50
0.42
0.40
0.20
0.10
0.80
20/33
20/30
0.60
0.66
0.34
0.05
1.25
20/200
20/25
20/400
20/16
Figure 5. Change in best spectacle-corrected visual acuity (BSCVA).
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Ophthalmology Volume 111, Number 4, April 2004
Figure 6. Distribution of best spectacle-corrected visual acuity (BSCVA)
before and after phototherapeutic keratectomy (PTK).
tion of undesirable vision disruption. Seven of 23 patients
had undergone prior interventions that failed to resolve their
vision impairments.
Macrostriae are full-thickness folds of the flap that occur
as a result of flap slippage that may occur secondary to
direct trauma, drying, and adhesion of the flap to the tarsal
conjunctiva, and the altered central convexity and stromal
support referred to as the “tenting effect.”16 Macrostriae are
best treated immediately. To remedy acute macrostriae, we
lift the involved area of the flap, most commonly the entire
flap. The flap is refloated with balanced salt solution and is
stroked gently and smoothed back into proper position,
taking care to remove any peripheral epithelium that would
become trapped in the interface.
If macrostriae are not recognized and treated immediately, however, the flap wrinkles become fixed and resistant
to smoothing. More aggressive maneuvers, such as stretching with forceps, suturing, hydration with hypotonic solutions, heating, and sandwich compression, have been proposed.5– 8,16 –18 These maneuvers are not without risk.
Figure 7. Distribution of uncorrected visual acuity (UCVA) before and
after phototherapeutic keratectomy (PTK).
744
Potential complications of these flap manipulations include
interface epithelial ingrowth, interface inflammation and
infection, tearing the flap edge, induction of new striae, and
creation of irregular astigmatism. The flap may seem to
improve initially, with later return of striae.
Phototherapeutic keratectomy also has been suggested
for chronic macrostriae with a 6-␮m ablation depth to
“make the (Bowman) membrane thinner and minimize its
‘mechanical memory.’”5 This technique differs from the
methodology used in our series.
In contrast to macrostriae, microstriae occur, despite
good flap repositioning. Microstriae are virtually universal
in LASIK flaps, although often they are invisible or optically insignificant. Vesaluoma et al19 detected microstriae in
60 of 62 eyes (96.8%) that had undergone LASIK using
confocal microscopy but in only 25 eyes (40.3%) that had
undergone LASIK by biomicroscopy. Our data suggest that
visually significant microstriae may be more prevalent in
patients with higher levels of myopic correction. After a
myopic laser photoablation, the bed is flatter. When the flap
is repositioned, it must conform to the altered contour. This
causes a relative compression of the anterior surface while
stretching the posterior surface of the flap, resulting in
microstriae at the level of Bowman’s and the anterior
stroma. In our series, the mean prerefractive surgery spherical equivalent was ⫺7.23 D (range, ⫺2.88 to ⫺13.55 D),
which probably exceeds the average level of myopic
LASIK, although we do not have data on the mean level of
myopia in all patients treated contemporaneously with the
patients who received PTK for striae. In our experience,
microstriae often do not respond to smoothing maneuvers or
to the other interventions discussed. Seven eyes had undergone specific procedures to remove the microstriae; all of
these procedures failed to relieve the symptoms.
The limited number of patients with data on flap thickness
precludes drawing a conclusion about whether a thin flap is
predisposed to developing striae. In 10 patients, corneal flap
thickness was available, with a mean flap thickness of 150 ␮m
and a wide range from 77 to 196 ␮m. Four of 10 patients
(40%) had a flap thickness of less than 135 ␮m. This suggests
that a thinner flap may be at increased risk of developing striae,
but a thicker flap is not immune from striae.
In 15 of 17 eyes (88%) for which data were available, the
vertical keratometric power was steeper than horizontal (P
⫽ 0.002). This finding may represent simply a preponderance of with-the-rule astigmatism before surgery. We cannot exclude the possibility that the corneal curvature plays a
role in the cause of visually significant striae, although our data
on keratometry (Table 1) do not suggest that the mean keratometry values deviated from a typical patient population.
Ten eyes (43%) had retreatment before development of
visually significant microstriae, suggesting that lifting (8
eyes) or recutting (2 eyes) a flap may have an increased risk
of developing striae compared with primary flap creation. In
contrast, 3 eyes with adequate flap thickness underwent
LASIK retreatment after PTK and did not develop new striae.
Formation of corneal haze after PTK on the flap was one
of our foremost concerns. Carones et al20 noted grade 3 and
4 haze formation in 82.3% of patients who underwent
photorefractive keratectomy (PRK) on top of a previous
Steinert et al 䡠 Phototherapeutic Keratectomy for Flap Striae
Table 5. Change in Refraction after Phototherapeutic Keratectomy
MR before Phototherapeutic
Keratectomy
MR after Phototherapeutic
Keratectomy
Analysis
Sphere
Cylinder
SE
Sphere
Cylinder
SE
Change
in SE
Change
in Cyl
Mean
Median
Standard deviation
Minimum
Maximum
0.00
0.00
0.94
⫺1.75
⫹2.00
⫺0.89
⫺0.75
0.52
⫺2.25
0.00
⫺0.45
⫺0.50
0.98
⫺2.50
⫹2.00
⫹0.80
⫹0.50
1.51
⫺1.75
⫹5.00
⫺0.75
⫺0.50
0.68
⫺2.50
0.00
⫹0.43
⫹0.25
1.40
⫺2.00
⫹3.75
⫹0.88
⫹0.75
1.21
⫺1.38
⫹3.88
⫹0.14*
⫹0.25*
0.83
⫺2.00
⫹1.50*
MR ⫽ manifest refraction; SE ⫽ spherical equivalent.
*Indicates a reducation in overall astigmatism.
Rojas and Manche22 used PTK on LASIK flaps for
treatment of anterior basement membrane dystrophy-related
epitheliopathy occurring after LASIK. Epithelial removal
was performed with placement of 20% alcohol for 30 seconds, followed by mechanical debridement and PTK. A
total of 6 pulses of laser were performed centrally (6.0-mm
optical zone) and another 6 pulses of laser peripherally
(3.0-mm optical zone). In their study of 10 patients, Rojas
and Manche noted 2 eyes with diffuse lamellar keratitis
stages 1 and 2 and another eye with trace corneal haze.22 All
of the above complications resolved over time. In our study,
diffuse lamellar keratitis did not develop in any eyes.
Phototherapeutic keratectomy for vision-impairing
chronic striae may seem undesirably aggressive because it
represents a permanent alteration of the flap. However, PTK
has the advantage of being the only intervention that directly reduces the optically disruptive elevations caused by
striae. By limiting the amount of tissue removed to the
ridges, we hypothesize that the stimulus for haze is minimized, whereas the PTK directly smoothes the optical surface to a level at which regrowth of epithelium is adequate
to mask the remaining optical irregularities.
For optically disruptive microstriae and for chronic macrostriae that do not respond adequately to the above intervention, the surgeon must determine that the epithelium has
been supported adequately and has been allowed to heal.
Epithelial hyperplasia between striae and hypoplasia over
the striae ridges often mask the optical disruption of the
striae. The first step in alleviating optically symptomatic
striae, therefore, is to encourage optimal surface integrity
with lubrication, punctal occlusion, consideration of an extended wear bandage contact lens in some cases, and time.
One study showed that the corneal epithelial thickness
peaks at the third month after LASIK in high myopes and
LASIK flap. Unlike PRK, which removes anterior flap
tissue to the depth necessary for the optical correction, PTK
for striae by our technique is intended to remove only the
elevated ridges of the striae, without violating most of the
anterior Bowman layer. Because of the frequent reapplication of masking fluid during PTK, much of the laser energy
was absorbed, and the depth of ablation cannot be calculated
from the number of pulses delivered. However, the small
hyperopic shift of 0.9 D, if performed as a PRK with a
6.5-mm optical zone, calculates to an ablation depth of less
than 11 ␮m. In the study by Carones et al, the deepest
ablation was 60 ␮m. Most patients in that series had excellent results at 1 month after PRK but a decline in vision and
marked haze formation at 3 to 10 months after PRK. Some
of the patients in our study were referred from long distances and were not available for long-term follow-up.
However, 15 eyes were followed up for more than 3
months, including 7 eyes that were followed up for more
than 6 months; late-onset haze did not develop in any of
these eyes. In 9 of 23 eyes, trace to 1⫹ haze developed
within the first postoperative month. Six of the 9 eyes with
haze were followed up for more than 90 days without any
evidence of haze progression. The 1 eye with loss of 1 line
of BSCVA had only trace haze; the loss of BSCVA was
believed to be the result of slight progression of myopic
macular degeneration. Development of haze did not correlate with either the total number of laser pulses or the
number of pulses applied to the stroma (Table 7).
Kapadia and Wilson21 reported transepithelial PRK for
optical correction after complicated flaps and caps in
LASIK. In their series, 1 patient had a 30-␮m cap and the
other had a 50-␮m flap. Transepithelial PTK was performed
followed by PRK. By this method, the cap and the flap were
completely ablated centrally. The authors reported no haze.
Table 6. Operative Parameters
Phototherapeutic Keratectomy Exposure
Flap and Stromal Bed Thickness
Analysis
Total
Pulses
Transepithelial
Phase
Stromal
Phase
Pachymetry At
Primary LASIK
Bed
Thickness
Flap
Thickness
Mean
Median
Standard deviation
Minimum
Maximum
286
288
42
163
348
196
211
54
60
289
95
91
50
31
223
563
548
37
517
632
416
430
35
337
444
150
155
40
77
196
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Ophthalmology Volume 111, Number 4, April 2004
Table 7. Laser Parameters, Follow-up Interval, and Corneal
Haze Rating
Eye
No.
Total
Pulses
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
240
235
245
321
300
321
256
306
286
288
342
283
268
289
341
286
263
318
303
266
163
308
348
286
288
42
163
348
Stromal
Phase
Pulses
57
48
90
32
121
117
91
67
123
223
44
62
142
31
112
93
91
62
97
189
95
91
50
31
223
Interval After
Phototherapeutic
Keratectomy
(days)
Haze after
Phototherapeutic
Keratectomy
262
235
222
58
125
204
75
354
193
211
131
30
112
66
48
84
117
106
78
60
105
105
105
129
106
80
30
354
Trace
Trace
1⫹
0
1⫹
0
0
0
0
0
Trace
0
0
Trace
Trace
0
0
0
1⫹
0
0
0
Trace
Mean
Median
Standard deviation
Minimum
Maximum
remains stable thereafter.23 Therefore, it may be advisable
to wait at least 3 months after LASIK to determine if the
symptoms attributable to striae are relieved. In some cases,
however, loss of vision may be so impairing that the functional needs of the patient justify earlier intervention.
If conservative measures fail, we believe that the results
of PTK as demonstrated in this series merits consideration
of PTK as the definitive intervention to ameliorate visual
disruption attributable to striae. The key elements in successful PTK on a LASIK flap are (1) determination of which
striae are optically significant by examination of the fluorescein tear pattern, the placido mires, and the effect of a
diagnostic contact lens refraction; (2) transepithelial treatment while monitoring fluorescence to determine when the
masking effect of the epithelium is diminishing; (3) limited
further PTK pulses using an artificial tear as a masking
agent, recognizing that the flap may be thin and that the goal
is reduction but not elimination of the striae; (4) postoperative support of the regenerating epithelium with administration of intensive lubrication.
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